1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly to a maintenance and recovery mechanism removing droplets and foreign matter remained and adhered to a droplet discharge section so that the discharge function of the droplet discharge apparatus is well maintained.
2. Description of the Related Art
As is well known, an image forming apparatuses such as a printer, a facsimile machine, a copier, and a multifunction peripheral having those functions includes a droplet discharge apparatus having a recording head including a droplet discharge head to discharge droplets such as ink.
In an apparatus discharging droplets such as ink, an image is formed by adhering or absorbing (impregnating) droplets discharged from a recording head onto or into a recording medium such a recording sheet while the recording medium is being fed.
In this case, the recording medium to be printed includes not only such a recording sheet but also any material to or into which a liquid can be adhered or absorbed, the material including fibers such as strings, leather, a metal, resin, glass, wood, ceramic and the like.
In such an image forming apparatus having the droplet discharge apparatus, ink retained on a nozzle surface of a droplet discharge head by surface tension of an ink meniscus is discharged (ejected) in a predetermined direction with a predetermined size by using a pressure caused by film boiling of ink or the like.
As a method of discharging droplets, there have been proposed a piezoelectric conversion method using a piezoelectric device, an electrostatic suction method using an electrostatic attractive force (see, for example, Japanese Patent Application Publication No. 2009-45870, “Patent Document 1”), a thermal conversion method such as bubble-jet (registered trademark) type (see, for example, Japanese Patent Application Publication No. 2007-290243, “Patent Document 2”) and the like.
On the other hand, at the droplet discharge head, a maintaining and recovering operation is generally performed. By performing the maintaining and recovering operation, it becomes possible to prevent ink remained and adhered to a nozzle surface of the droplet discharge head from being thickened and avoid that ink is discharged in the direction other than a predetermined direction, that ink has a size other than a predetermined size, and that the meniscus of ink is destroyed (deformed) due to the ingress of foreign matter into the nozzle.
As an example of a structure performing the maintaining and recovering operation, a cap is used for sealing a nozzle surface of a liquid discharge head and a negative pressure is applied to the inside of the cap to suction ink from the nozzle (see for example, Japanese Patent No. 4149821, “Patent Document 3”).
Further, as an example of a structure suctioning ink from the inside of the cap and cleaning the discharge head, a carriage is slightly moved during the suction operation so as to form a gap at a part of the cap to generate air flow within the cap to flow ink absorbed in an ink absorbing body from the nozzle surface to the absorbing section. Then, the nozzle surface is wiped by a wiper made of an elastomer material. By doing this, the nozzle surface is cleaned and the meniscus of ink in the nozzle is recovered (see, for example, Japanese Patent Application Publication No. 06-126947, “Patent Document 4”).
However, in a case where ink accumulated in the nozzle or on the nozzle surface is suctioned in a manner as disclosed in Patent Document 3, when the cap is separated from the nozzle surface while the negative pressure is still large, a sudden pressure change may occur, and due to the sudden change of the pressure, the meniscus in the nozzle may be destroyed (deformed).
On the other hand, when the structure disclosed in Patent Document 4 is used, it may become easier to flow ink retained in the ink absorbing body. However, if the gap is not properly generated, a large amount of ink may be retained on the nozzle surface and the large amount of ink may be adhered to the wiper when the wiper wipes the ink. Because of this feature, when the ink adhered to the wiper is left for a long period, the ink may be thickened or may be fixed to the wiper. As result, the thickened or fixed ink may block the wiping capability of wiping the nozzle surface. In this case, the contacting area between the wiper surface and the nozzle surface may become smaller, thereby reducing the efficiency of removing ink from the nozzle surface. This phenomenon may affect the meniscus of ink and block normal discharging operation, which may degrade the quality of print data, increase maintenance cost of the wiper, and affect the maintenance and recovery mechanism of the apparatus.
Further, the gap to be formed at a part of the cap is formed while the cap is inclined against the nozzle surface due to the slight movement of the carriage. In this case, in order to ensure the sealing and adhesion performance between the cap and the nozzle surface, a flexible material such as elastomer is generally used. Because of this feature, for example, after the slight movement is repeated for a long period, the shape of the flexible material may not be easily recovered (i.e., the shape of the flexible material may be deformed), thereby making it difficult to maintain the sealing and adhesion performance.
On the other hand, ink retained on the surface of the nozzle surface is once absorbed (suctioned) into the ink absorbing body provided in the cap. After a certain time interval, the absorbed ink is further suctioned. Therefore, due to the time interval, ink may be thickened or fixed before being suctioned. In this case, the suctioning function may not be appropriately maintained.
Further, it may be required to fill the cap with ink in advance in order to remove ink retained on the nozzle surface. However, to fill the cap with ink, the suction operations is always required to be performed to withdraw ink from the inside of the nozzles. Because of this feature, ink filled in the cap may be unnecessarily wasted and ink consumption amount may be increased.
Next, with reference to FIGS. 1 through 4, a problem is described which may be occurred when such a method as disclosed in Patent Document 4 is used where a wiper wipes ink.
Conventionally, to perform the maintaining and recovering operation on the nozzles of the droplet discharge head, as schematically illustrated in FIG. 1, a cap B being in close contact with a nozzle surface A1 of a droplet discharge head A is used as a sealing member. Further, while the cap B is in close contact with the nozzle surface A1 of the droplet discharge head A, a negative pressure is applied to the inside of the cap B using a suction mechanism (not shown), so that droplets (i.e., ink L and foreign matter) are suctioned from nozzles A2.
After ink is suctioned from the nozzles A2, the cap B is separated from the nozzle surface A1 of the droplet discharge head A. As a result, as schematically illustrated in FIG. 2, a large amount of ink L′ withdrawn from the inside of the nozzles due to the negative pressure applied to the inside the cap A remains on the nozzle surface A1 of the droplet discharge head A in dorm shapes or in a combined shape.
Then, as schematically illustrated in FIG. 3, the remaining ink is wiped off by using a wiper C made of a material such as an elastomer. In this case, however, as schematically illustrated in FIG. 4, when the wiped ink is left on the wiper C for a period of time, the ink remaining on the wiper C may be thickened or fixed to the wiper C, which may block the further wiping operation. As a result, once the ink is thickened or fixed to the wiper C, ink on the nozzle surface A1 of the droplet discharge head A may not be sufficiently removed with the wiper C.
As described above, when a method as described in Patent Document 4 is used, when ink is suctioned to recover the meniscus of ink in the nozzle and ink remained on the nozzle surface is moved at the same time, there may arise a problem in further wiping operation and a problem in further suction operation.